Possible fix for DIRMINA-79 - The number of ThreadPoolFilter threads sometimes becomes 0.
* Fixed a bug that the thread can die when interrupted in Worker.waitForPromotion() and Worker.fetchBuffer()
* Fixed deadlock while shutting down.
* Fixed DIRMINA-79 - The number of ThreadPoolFilter threads becomes 0 sometimes.
** Fixed problems in giveUpLead() and fetchBuffer()